A conventional angular velocity sensor is disclosed in Japanese Patent Laid-Open Publication No.11-351874.
FIG. 13 is a perspective view of the conventional angular velocity sensor. First detecting electrodes 2 are provided on side surfaces of a first oscillator 1 made of e.g. quartz, and first driving electrodes 3 are provided on a front surface. Similarly, second detecting electrodes (not shown) are provided on side surfaces of a second oscillator 4, and second driving electrodes 5 connected to the first driving electrodes 3 on the first oscillator 1 are provided on the front surface. A joint 6 unitarily connects the first oscillator 1 to the second oscillator 4 at their respective ends. Driving wires 7 are electrically connected at respective one ends to the first driving electrodes 3 and the second driving electrodes 5, and are connected at respective other ends to two driving terminals 8. Detecting wires 9 are electrically connected at respective one ends to the first detecting electrodes 2 and the second detecting electrodes (not shown), and are connected at respective other ends to two detecting terminals 10.
An operation of the conventional angular velocity sensor will be explained.
When the first driving electrodes 3 and the second driving electrodes 5 are fed via the driving wires 7 with an alternating-current voltage from the driving terminals 8, the first oscillator 1 and the second oscillator 4 start oscillating along the Y axis. Then, as the angular velocity sensor is urged at an angular velocity about the Z axis, a Coriolis force is developed on the first oscillator 1 and the second oscillator 4 and deforms the first oscillator 1 and the second oscillator 4 along the X axis. The deformation generates a charge to be output through the first detecting electrode 2 and the second detecting electrode (not shown). The charge is then transferred via the detecting wires 9 and the detecting terminals 10 to a computer (not shown) which determines an angular velocity.
When the first oscillator 1 and the second oscillator 4 are not balanced in weight, they may deform along the X axis due to the unbalance weight even if the angular velocity sensor is not applied an angular velocity to. This causes a charge to be generated on the first detecting electrode 2 and the second detecting electrode (not shown).
For balancing the weight between the first oscillator 1 and the second oscillator 4 in the conventional angular velocity sensor, a rewter 11 grinds edges of the second oscillator 4 and the joint 6 to make a desired size of ground portion 12, as shown in FIG. 14.
Since the rewter 11 spins to grind the edges of the second oscillator 4 and the joint 6 in the conventional angular velocity sensor to make the ground portion 12, a small eccentric movement of the rewter may cause the ground portion 12 to be finished with a surface roughened as course as about 5 μm. The angular velocity sensor accordingly produce a voltage of substantially ±10 mV when no angular velocity is applied, as shown in Table 1, hence declining output characteristics of the sensor.
TABLE 1Surface RoughnessOutput Voltage withRmax (μm)No Angular Velocity (mV)Sample 14.8+6.2Sample 24.6+8.2Sample 34.9+9.4Sample 44.7−7.1Sample 54.7−5.4